1. Field of the Invention
The invention relates to wavelength division multiplexed optical systems in general and, more particularly, to bidirectional wavelength division multiplexed optical communication systems having a bidirectional waveguide configured to carry two counterpropagating WDM optical communication signals and at least two counterpropagating optical service channels.
2. Description of the Related Art
As the need for communication signal bandwidth increases, wavelength division multiplexing (WDM) has progressively gained popularity for multiplying the transmission capacity of a single optical fiber. A review of optical networks, including WDM networks, can be found in Ramaswami et al., Optical Networks: A Practical Perspective (Morgan Kaufman,(copyright) 1998), the disclosure of which is incorporated herein by reference. Typically, wavelength division multiplexed optical communication systems have been designed and deployed in the long-haul, interexchange carrier realm. In these long-haul optical systems, a wavelength division multiplexed optical communication signal comprising plural optical channels at different wavelengths travels in a single direction on a single fiber (unidirectional transmission). Because the communication traffic in such systems commonly travels many hundreds of kilometers, the need for add-drop multiplexing of individual channels is infrequent, occurring at widely-spaced add-drop nodes.
Although unidirectional WDM optical systems are suitable for conventional long-haul interexchange carrier markets, metropolitan (local) communications systems typically involve extensive routing and switching of traffic among various nodes positioned within optical fiber rings. Consequently, smaller metropolitan markets require considerably more extensive add-drop multiplexing in order to successfully implement wavelength division multiplexing in their short-range systems. Further, in order to maximize the effectiveness of wavelength division multiplexing in these local areas, it would be useful to implement bidirectional WDM optical systems, e.g., to enhance network design flexibility and minimize the number of optical fibers needed to implement work and protect systems. In a bidirectional WDM system counter-propagating WDM optical signals, each comprising a number of optical channels, are carried on the same waveguiding medium, such as a single optical fiber. Implementation of a bidirectional system requires several considerations not present in conventional unidirectional optical systems. Add-drop multiplexing in a bidirectional optical environment becomes considerably more complex since optical channels must be selected from each of the counter-propagating WDM optical signals. In addition to the difficulties posed by add-drop multiplexing channels from two counter-propagating WDM optical signals, there must also be techniques for directing optical service channels to various locations within the bidirectional network.
In U.S. Pat. No. 6,111,675, a system is disclosed for the bidirectional transmission of telemetry service signals using a single optical fiber. In a first configuration, one wavelength is used as a service channel in a first direction while a second wavelength is used as a service channel in a second direction. In a second configuration, termed a xe2x80x9cwalkie-talkiexe2x80x9d technique, the same wavelength is used as a service channel in two directions. A complete telemetry service channel is launched in one direction followed by sending a complete service signal in the opposite direction; alternatively, the service signal messages are divided into segments which are alternately sent in two directions. While these techniques appear to have utility in long-haul optical systems, it would be useful to have a bidirectional wavelength division multiplexed optical communication system configured for systems requiring high volumes of optical add-drop multiplexing and which include a bidirectional optical service channel. Such a system could be advantageously employed in local, metropolitan networks.
The present invention provides a bidirectional wavelength division multiplexed optical communication system having bidirectional optical service channels. The bidirectional WDM optical communication system includes a bidirectional optical waveguide configured to carry a bidirectional optical communication signal comprising counterpropagating WDM optical signals. Each WDM optical signal includes plural optical channels and an optical service channel. A bidirectional optical add-drop multiplexer optically communicates with the waveguide. A first optical service channel selector optically communicates with the first bidirectional optical add-drop multiplexer input/output port. The first optical service channel selector is configured to separate the first optical service channel from the first WDM optical communication signal such that the first WDM signal enters the first input/output port of the bidirectional optical add-drop multiplexer and the first optical service channel is routed to a service channel module. Similarly, a second optical service channel selector optically communicates with the second input/output port of the bidirectional optical add-drop multiplexer. As with the first service channel selector, the second optical service channel selector separates the second optical service channel from the second wavelength division multiplexed optical communication signal such that the second wavelength division multiplexed optical communication signal enters the second input/output port of the bidirectional optical add-drop multiplexer and the second optical service channel is routed to the service channel module.